Suction air filter

ABSTRACT

A suction air filter for an internal combustion engine of a hand-held working tool has a housing having an inlet opening for air sucked in and an outlet opening for the clean air exiting the suction air filter and supplied as combustion air to a suction channel of the internal combustion engine. The housing includes a plurality of filter chambers arranged in series one after another in a direction of air flow from the inlet opening to the outlet opening. Each one of the filter chambers has at least one filter body positioned therein through which filter body the air flows.

BACKGROUND OF THE INVENTION

The present invention relates to a suction air filter for internalcombustion engines of a hand-operated working tool like a cut-off toolor the like with a housing being provided with an inlet opening forintake air and an outlet opening for clean air which is supplied ascombustion air to the suction channel of the internal combustion engineand being provided within the housing with a filter body between theinlet opening and the outlet opening.

Such a suction air filter for a hand-operated working tool is known fromU.S. Pat. No. 5,073,307. A carburetor sucks clean air into a suctionchannel for producing the fuel/air mixture whereby the supplied air iscleaned from dirt particles of the intake air in an air filter locatedupstream of the carburetor. The filter body of the air filter isconstructed as a ring filter. The intake air enters the filter from theouter mantle surface. Dirt particles are filtered by the filter from thecontaminated intake air. A radially inwardly directed air flow iscreated because of the pressure difference between outer and inner sideof the ring filter. The cleaned air within the interior space of thering filter is supplied to the suction channel of the carburetor via anoutlet opening of the air filter. Such a ring filter must provide a highfilter action, particularly if installed in working tools like cut-offtools, in order to be able to effectively filter the dirt particles,which are created during operation of the working tool, from the intakeair and thus to prevent a contamination of the carburetor and anincreased wear of the internal combustion engine. The application ofvery fine-pored filters, however, only provides a very short servicelife due to the rapid clogging of the filter pores since the filteraction decreases considerably and, moreover, the pressure within thesuction channel decreases considerably so that a loss of performance isto be expected.

On the other hand, the application of large-pored filters carries therisk that fine and finest dirt particles pass through the ring filterunimpededly and deposit within the interior of the carburetor and of thecombustion engine, possibly leading to permanent damage.

Moreover, when removing the air filter for maintenance and cleaningpurposes, there is a risk that small and large dirt particles can enterthe exposed suction channel of the carburetor.

It is, therefore, an object of the invention to keep the pressure dropwithin the air filter as low as possible during a longer service life ofthe working tool and to increase the service life of the air filter.

SUMMARY OF THE INVENTION

A suction air filter for an internal combustion engine of a hand-heldworking tool according to the present invention is primarilycharacterized by:

a housing having an inlet opening for air sucked in and an outletopening for the clean air exiting the suction air filter and supplied ascombustion air to a suction channel of the internal combustion engine;

the housing comprising a plurality of filter chambers arranged in seriesone after another in a direction of air flow from the inlet opening tothe outlet opening; and

wherein each one of the filter chambers has at least one filter bodypositioned therein through which filter body the air flows.

Preferably, the housing has a first, a second, and a third one of thefilter chamber in the direction of air flow, wherein the filter body ofthe first filter chambers is a prefilter, the filter body of the secondfilter chamber is a main filter, and the filter body of the third filterchamber is a fine filter.

An upstream side of one of the filter bodies is preferably positionedsubstantially in a plane defined by the vector of the gravitationalforce and a line extending perpendicular to the direction of air flow.

The filter chambers are connected to one another to as to be sealedagainst introduction of external air.

The filter chambers are detachably connected to one another.

The housing expediently comprises a housing cover and the first filterchamber is delimited by the housing cover and a housing wall of thesecond filter chamber.

Advantageously, the housing wall of the second filter chamber has aplurality of air-flow openings.

The air-flow openings are expediently distributed uniformly over theentire surface area of the housing wall.

Preferably, the housing wall of the second filter chamber has acircumferential sealing groove. The housing cover has a partition fordelimiting the first filter chamber. The circumferential groove receivesan edge of the partition.

The second filter chamber preferably comprises a cup-shaped chamberhousing with an inner circumferential shoulder at which the filter bodyof the second filter chamber is supported in an air-tight manner.

In a preferred embodiments of the present invention, the filter body ofthe second filter chamber comprises a sealing member made of a foamedplastic material, the sealing member resting air-tightly on theshoulder. The sealing member is preferably made of polyurethane.

Advantageously, the third filter chamber is comprised of a cup-shapedend housing with a circumferential support edge for receiving the filterbody of the third filter chamber. The cup-shaped end housing is providedwith the outlet opening.

Advantageously, the filter body of the third filter chamber comprises acircumferential U-shaped sealing rim that engages the support edge in anair-tight manner.

The filter body of the third filter chamber comprises a reboundcontainer for rebounding fuel particles, arranged at a side of thefilter body of the third filter chamber facing the outlet opening so asto be positioned opposite the outlet opening.

The sealing rim is preferably sealingly engaged by the sealing member ofthe filter body of the second filter chamber.

The cup-shaped end housing expediently has a sealing surface facing thesecond filter chamber and wherein the sealing member rests sealingly onthe sealing surface.

In yet another embodiment of the present invention, the cup-shapedchamber housing comprises fastening means for fastening the cup-shapedchamber housing to the cup-shaped end housing, wherein the fasteningmeans are accessible only after removing the housing cover.

The housing cover has a air suction channel for guiding the air suckedin to the first filter chamber, the air suction channel having reboundwalls for separating coarse dirt particles from the air flow.

The inlet opening is located, when viewing the housing cover in an endview, within the area enclosed by the periphery of the housing cover.

By means of the serial arrangement of several filter chambers eachprovided with a filter body, the cleaning of the air is carried outstepwise with the degree of cleanness of the air increasing fromfiltering step to filtering step. By providing separate filter chambers,depositing spaces for dust are provided into which dirt particles whichbecome loose by vibration can fall due to their own weight. Thus, it isensured that the filter bodies clog less rapidly even at a longerservice life of the working tool. Moreover, the contamination level ofthe filter bodies decreases more and more from one filtering step to thenext so that when maintenance work is done, first the filters at thedirt side have to be cleaned whereas the filters at the clean air sidehave to be cleaned at considerably larger time intervals because oftheir considerably lower contamination level. Moreover, because of thestepwise maintenance of the filters located remote from the carburetor,a protection for the suction channel of the carburetor is given duringcleaning, as long as the last filter abutting the suction channel is notremoved.

Moreover, during the maintenance work the maintenance person has avisual control of the contamination level of the respective filter to beserviced and thus can determine whether the cleaning, respectively, theexchange of the subsequent adjacent filter and the extra work requiredtherefor is necessary at all.

In a preferred embodiment filtering is carried out via three filterbodies arranged in a serial arrangement, a prefilter, a main filter anda fine filter. The prefilter is expediently located in a housing coverwhich can be easily removed and which is provided with air suctionchannels for supplying the intake air. The air suction channels areadvantageously arranged angularly relative to the air flow direction ofthe air flowing through the air filter. The intake air after havingpassed through the air suction channels is advantageously deflected inthe direction of the prefilter by rebound walls provided within thefilter chamber of the prefilter. Thus, large dirt particles lose theirkinetic energy and fall into the depositing spaces of the filter chamberdue to their own weight without clogging the filter body of theprefilter. Large dirt particles which have collected on the upstreamside of the filter body fall down in the same manner; this process isencouraged by the fact that the upstream side of the filter body islocated in a plane which is defined by the vector of the gravitationalforce and a line perpendicular relative to the air flow direction sothat the upstream side of the filter body is positioned approximatelyvertically when the working tool is not operated. Large dirt particlescan therefore fall down unimpededly.

For preventing air leaks, i.e., unwanted external air streams enteringthe filter chambers, the filter chambers are connected to one anotherair-tightly, advantageously detachably. Thus, a clearly defined air-flowdirection is created from the outer filter chamber located at the dirtside (upstream side) to the inner filter chamber located at the cleanair side (downstream side) of the suction air filter.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the present invention will appear moreclearly from the following specification in conjunction with theaccompanying schematic drawings, in which:

FIG. 1 illustrates a schematic side view of a cut-off tool with aninventive suction air filter;

FIG. 2 illustrates a cross-sectional side view of the air filterarranged at the carburetor and provided with prefilter, main filter andfine filter, arranged in series;

FIG. 3 a plan view in cross-section of the illustration according toFIG. 2;

FIG. 4 a side view of the prefilter housing cover in a differentembodiment; and

FIG. 5 a plan view of the housing cover according to FIG. 4.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates a side view of a cut-off tool. The cutting wheel 65is driven by an internal combustion engine 66, for example, a two-strokeengine. The ignitable fuel/air mixture is supplied to the engine 66 bythe carburetor 1, for example a diaphragm carburetor that sucks in cleanair 10 by means of its suction channel 7, see FIG. 2. The clean air 10is being filtered within the air filter 2 that is attached to thediaphragm carburetor 1 and that comprises, in the illustratedembodiment, three filter segments 11, 12, and 13 in a staggered (serial)arrangement within housing 3. When the combustion engine is inoperation, intake air 8 flows into the air filter 2 via inlet openings 5and air suction channels 31, due to the creation of underpressure withinthe suction channel 7 of the diaphragm carburetor. The intake air 8successively flows through the filter bodies 11, 12, and 13, and thedegree of cleanness of the intake air increases from filtering step tofiltering step. After passing through the third filter body 18, theintake air is sufficiently clean and flows into the suction channel 7 asclean air 10 via an outlet opening 6 in order to be mixed with fuel toproduce a fuel/air mixture in a manner known per se.

According to the invention, the air filter comprises filter segmentseach having a filter body arranged in a separate filter chamber. Thefilter segment operate completely independently from one another, incase of a failure of one filter segment, the intake air is being cleanedby the filter action of the filter segment arranged upstream ordownstream thereof.

In the embodiment according to FIGS. 2 and 3, the three filter segmentsare in the form of the prefilter 11, main filter 12, and fine filter 13,with the filter action increasing from filter segment to filter segment.Each of the three filter segments has its own filter chamber 15, 17 and19 into which a respective filter body 14, 16, 18 is inserted.

The filter chamber 15 is laterally delimited by a wall 55 of the housingcover 4. This wall 55 is located within the interior space created bythe outer wall 59 and is formed as a unitary part thereof. In theair-flow direction, the filter chamber 15 is deliminted at one side bythe back wall 62 of the housing cover 4 and at the other side by ahousing wall 54 of the adjacent filter chamber 17 of the main filter 12.The filter body 14 of the prefilter 11 is arranged within the filterchamber 15 in the interior space of the housing cover 4 andadvantageously consists of a porous foamed material which can, accordingto FIGS. 2 and 3, be designed of two layers 23 and 24 of differentporosity with the layer 23 located upstream, viewed in the air flowdirection, being of a coarser porosity than the successive layer 24. Thefilter body 14 can expediently also be designed of a single layer or ofmore than two layers.

The contaminated intake air 8 flowing into the housing cover 4 throughthe inlet opening 5 and the air suction channel 31 passes through thefilter body 14 of the prefilter 11 due to the pressure differencebetween the intake air side and the clean air side of the air filter 2;during this process, large dirt particles fall down due to their ownweight at the upstream side 20 of the filter body 14 and collect at thedirt side of the filter chamber 15. In order to encourage this effect,the upstream side 20 of the filter body 14 is embodied as a planar,vertically extending surface which is defined by the vector at thegravitational force 52 and any line 53 perpendicular relative to the airflow direction 9, FIGS. 2 and 3. Accordingly, the upstream side 20 ispositioned approximately perpendicularly relative to a horizontal basesurface across which the tool is moved during operation, and large dirtparticles can fall straight down.

In a further expedient embodiment it is provided that the intake air 8flowing into the housing cover 4 enters the prefilter 11 angularlyrelative to the air flow direction 9. As can be seen in FIG. 3, the airsuction channel 31 with its inlet opening 5 is located laterally at thehousing cover 4 at an angle of approximately 100° relative to the airflow direction 9, preferably in the upper lateral area in order toprevent sprayed water from possibly entering the air suction channel.The intake air 8 drawn in through the air suction channel 31 hitsrebound walls 22 which are designed such that the incoming air isdeflected toward the air flow direction 9. It thus hits the upstreamside 20 of the prefilter 11 perpendicularly. Large dirt particlescarried by the intake air 8 lose their kinetic energy by hitting therebound walls 22 and precipitate from the air flow into depositingspaces 51 within the prefilter chamber 15 from which collected dirt canbe easily removed during cleaning. The depositing spaces 51 are locatedbetween the rear wall 62 of the housing cover 4 and the upstream side 20of the filter body 14 of the prefilter 11. The depositing spaces 51 areseparated from one another by laterally projecting, horizontally andvertically extending stays 58 which are formed as one piece with theexterior wall of the housing cover. The free end faces of the stays 58support the filter body 14. At the side facing the main filter 12, thefilter body 14 rests on supporting stays 67 which are provided at thehousing wall 54 and extend in the vertical direction.

Advantageously, the housing cover 4 is removably attached to the chamberhousing 34 of the main filter 12 by means of a wing screw 21. Thethreaded bolt 35 of the wing screw 21 protrudes through a bushing 36which is formed as one piece with the housing cover 4 and extends overmost of the depth of the housing cover 4 from the rear wall 62 of thehousing cover 4 to the adjacent chamber housing 34 of the main filter12. In the housing wall 54, facing the prefilter 11, of the chambercasing 34 a receiving portion 37 is provided into which a threaded partcan be screwed or a nut can be inserted for receiving the threaded bolt35 of the wing screw 21. Thus, the housing cover 4 can be unscrewed byhand without applying tools, which allows a fast visual control and aneasy manipulation for cleaning and maintenance of the air filter.

The bushing 36 protrudes through the filter body 14 of the prefilter 11and in conjunction with a second bushing 38, also connected to thehousing cover 4 as a unitary part and advantageously located away fromthe vertical and horizontal center planes, provides a clear definitionof the fitting position of the filter body 14. Therefore, the filterbody 14 which must be provided with two corresponding bores or openings39 and 40 can only be inserted into the filter chamber 15 in the exactlydefined position. This precludes that the filter body is inserted in awrong position.

The housing cover 4 is connected air-tightly to the chamber housing 34of the main filter 12. For this purpose, an edge 41 of the partition 55of the filter chamber 15 is formed as one piece with the housing cover 4and engages a circumferential groove 42 of the chamber housing 34 of themain filter 12. A rubber gasket 43 is inserted into the circumferentialgroove 42. After the housing cover 4 is screwed onto the chamber housing34 by means of the wing screw 21, the filter chambers 15 and 17 of theprefilter 11, respectively, the main filter 12 are hermetically(air-tightly) sealed toward the exterior so that the risk of air leaks(introduction of external air) is excluded and a definite air-flowdirection of the air to be cleaned is given according to arrow 9.

FIGS. 4 and 5 illustrate a different embodiment of the housing cover 4with the prefilter 11; the same reference numerals apply to the samestructural members. In this embodiment, two air suction channels 31 areprovided which are symmetrical relative to the longitudinal center axis50 (FIG. 5). The air suction channels 31, extending across a major partof the structural height of the housing 4, are located at an angle ofapproximately 180° relative to the air-flow direction 9 with the inletopenings 5 being provided at that side of the housing cover 4 facing themain filter 12. The intake openings 5 are located when viewing thehousing cover 4 in an end view within the periphery of the housing cover4, wherein the lateral circumferential outer wall 59 surrounds thenarrow sides as well as the longitudinal sides of the air suctionchannels 31. The air suction channels 31 project past the end face 60 ofthe outer wall 59 so that the inlet openings 5 are positioned outside ofthe outer housing cover wall under the cover 100 of the tool (FIG. 1).In the mounted position, the inlet openings 5 are located at the levelof the housing wall 54 of the chamber housing 34 of the main filter 12.

The intake air 8 flows through the air suction channels 31 and is firstdeflected by 90 degrees at the interior surface of the housing cover 4according to arrow 32 and subsequently hits rebound walls 22 whichdeflect the intake air toward the air flow direction 9 and forces it toflow through the filter body 14. Due to the double deflection of theintake air flow on its way through the suction channels 31 to the filterbody 14, it is ensured that in particular large dirt particles which arebeing carried in the air flow lose their kinetic energy through theimpact at the housing wall, respectively, at the rebound wall 22 so thatthe precipitate by their own weight and deposit at the bottom of thefilter chamber 15, respectively, within the depositing spaces 51 of thehousing cover 4.

In the embodiment according to FIGS. 4 and 5, the housing cover 4 isprovided with a bore for attaching it to the chamber housing casing 34of the main filter 12. A wingscrew 21 for connecting the housing coverand the casing of the main filter can be inserted into the bore. Abushing receiving the threaded bolt of the wing screw can be omitted sothat the manufacture of such a housing cover is technologically verysimple.

After flowing through the prefilter 11, the pre-cleaned air enters themain filter 12 which consists of the filter chamber 17 and the filterbody 16 provided therein. The main filter chamber 17 is delimited towardthe exterior by a cup-like chamber housing 34. In the air-flow direction9, at the dirt side (upstream side) of the main filter, the housing wall54 is provided with numerous air-flow openings 33 which are evenlydistributed across the entire wall surface and through which air canflow into the filter chamber.

In the illustrated embodiment the main filter body 16 is a folded filterwith numerous folded lamellas 25. As can be seen in FIG. 3, the foldedlamellas 25 of the folded filter 16 are designed to be approximatelyvertical relative to the rest position of the tool and extend in thelongitudinal direction of the air filter in air-flow direction 9. Thus,the folded lamellas 25 are arranged approximately at a plane 61 that isdefined by the air-flow direction 9 and the vector 52 of the gravitionalforce, FIG. 2.

On flowing through the folded filter 16, dust and dirt particles of theair to be cleaned deposit within the spaces being formed by two adjacentfolded lamellas 25. Due to the force of gravity, large dirt particleswill precipitate from these spaces and collect at the bottom of thefilter chamber, respectively, will gradually deposit from the bottomupwards within the spaces of the folded filters during an extendedperiod of operation of the tool so that for a partial contamination ofthe main filter a sufficient filter surface for cleaning the air stillremains, thereby also keeping the pressure difference low. Moreover,after unscrewing the housing cover 4 it can be visually determined bythe level of dirt within the spaces whether the main filter has to becleaned or exchanged. The visual control is performed from the outsidethrough the air-flow openings 33 within the housing wall 54 withoutremoving the chamber housing 34; due to their even distribution, theair-flow openings 33 allow a view of the entire filter surface of thefilter body 16. In case that cleaning is necessary, the chamber housing34 is removed and deposited dirt can easily be removed from the spacesof the folded filter and from the bottom of the filter chamber 17.

At the interior side of the chamber housing 34, a circumferentialshoulder 57 is provided by which a step 63 is formed pointing in thedirection of the upstream side of the main filter; the filter body 16can be mounted air-tightly onto the step 63. For this purpose the filterbody 16 is expediently provided at the upstream side with acircumferential sealing member 26 which is preferably manufactured ofpolyurethane foam and which provides a circumferential recess at theouter surface and rests on the shoulder 57.

The cup-shaped end housing 44 in which the filter chamber 19 and thefilter body 18 of the fine filter are located, adjoins the chamberhousing 34. The end housing 44 is provided with a circumferentialsupport edge 29 that faces the main filter and onto which the finefilter 13 can be mounted. The filter body 18 of the fine filter isdelimited by a circular, U-shaped sealing rim 27 which is designed as asealing groove 28 and is expediently manufactured of a soft plasticmaterial or of rubber. In the mounted position of the fine filter, thesupport edge 29 of the end housing 44 engages the sealing groove 28air-tightly. This prevents air leaks between the downstream side and theupstream side of the fine filter. The sealing (foam) member 26 of thefilter body 16 forms a support frame which encloses the sealing member27 of the filter body 18 and by which the filter chamber 19 is sealedhermetically toward the exterior. In the direction of the air flow 9,the filter chamber 19 is thus delimited at the upstream side by thefilter body 16 and at the downstream side by the cup-shaped end housing44 which is provided with the outlet opening 6 at its free end. Theexterior wall of the end housing 44 extends approximately parallel tothe filter surface of the filter body 18 and overlaps the filter body 18in the lower area with its support edge 29. Fine dirt particles havingpassed through the fine filter hit the exterior wall of the end-casing44 and can deposit within the further depositing space 64 in the area ofthe bottom 56 of the end housing.

The filter body 18 advantageously consists of a flock-coated wire clothand is able to filter finest particles from the air flow by means ofelectrostatic charging and by its fine-meshed structure.

As can be seen in FIG. 3, the main filter chamber housing 34 is attachedto the end housing 44 of the fine filter 13 by screws 45. By the forceof the screw connection, a sealing surface 46 extending circularly aboutthe end casing 44 is pressed against the sealing member 26 of the filterbody 16 such that the chamber housing 34 and the end housing 44 areconnected air-tightly. The screw connection must only be unscrewed whenmaintenance of the main filter 12 is necessary. When the screwconnection is unscrewed, the filter body 18 remains in its mountedposition and thus protects the suction channel 7 from possiblecontaminations from the exterior. Advantageously, the screw connectionis only accessible when the housing cover 4 of the prefilter 11 has beenremoved, in order to ensure that the chamber housing 34 will beunscrewed only after checking the contamination level of prefilter andmain filter. It may also be advantageous to provide a quick actingclosure or the like particularly easily accessible from the outsidebetween main filter, chamber housing 34 and end housing 44.

A rebound container 30 is provided within the filter body 18 at thedownstream side, approximately at the level of the outlet opening 6. Therebound container 30 is designed to catch fuel particles which may, whenthe intake channel is closed, be repulsed through the suction channel 7by the piston of the combustion engine and which can lead to aninability of the fine filter to function when the filter body it wetted.The rebound container 30 is formed by a container plate 47 which isshaped convexly in the direction of the outlet opening 6 and which hasapproximately the same diameter as the outlet opening 6. At itscircumference, the container plate 47 is surrounded by a container wall48 which is designed to prevent a swirling of the repulsed flow of fuelparticles and which guides the fuel particles into the rebound container30. At its upper side, the container wall 48 has an open segment of anangular extension of approximately 60° so that even fuel particles beinglocated above the rebound container precipitate downwardly. A pin 49 forfacilitating removal of the filter body 18 from the filter chamber 19 isprovided at the side of the filter body 18 opposite the reboundcontainer.

Like the upstream side 20 of the prefilter 11, the upstream sides ofmain filter 12 and fine filter 13 are each positioned in a plane whichextends downwardly, approximately vertically, when the tool is in itsrest position so that large dirt particles can simply fall down from thesurface of the filter body. This also ensures that the air to be cleanedflows through all three filters in a straight flow path without beingdiverted (air flow direction 9). Due to the uniform flow, the pressuredrop within each filter segment and thus within the entire air filter iskept as low as possible. The particles carried by the air flow have arelatively uniform structure due to the deposition of large dirtparticles at the rebound walls of the prefilter and at the upstreamsides so that the filter bodies are evenly contaminated with dirt anddust. This increases the service life of the air filter.

The degree of cleanness of the air having passed through the fine filter13 amounts to more that 99%. This clean air is guided as combustion air,via the end housing 44 which is tapered conically in the directiontoward the outlet opening 6, to the suction channel 7 of the diaphragmcarburetor in which the combustion air is mixed with fuel to form afuel/air mixture.

At the clean air side of the fine filter 13 the end 44 canadvantageously be provided with an opening through which a connectingtube can be inserted for pressure compensation between the dry surfaceof the regulating diaphragm of the diaphragm carburetor and the cleanair side. An underpressure which builds up at the clean air side of theair filter when the contamination of the filter body increases, has acompensating effect on the regulating diaphragm so that he fuel supplyis reduced according to the amount of in-flowing combustion air and theair/fuel ratio is kept substantially at a constant level.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

What we claim is:
 1. A suction air filter for an internal combustionengine of a hand-held working tool; said suction air filter comprising:ahousing having an inlet opening for air sucked in and an outlet openingfor the clean air exiting the suction air filter and supplied ascombustion air to a suction channel of the internal combustion engine;said housing comprising a plurality of filter chambers arranged inseries one after another in a direction of air flow from said inletopening to said outlet opening; wherein each one of said filter chambershas at least one filter body positioned therein through which filterbody the air flows; wherein said housing comprises at least a first, asecond and a third one of said filter chambers, wherein said filter bodyof said first filter chamber is a prefilter, said filter body of saidsecond filter chamber is a main filter, and said filter body of saidthird filter chamber is a fine filter; wherein said housing comprises adetachable housing cover and wherein said first filter chamber isdelimited by said housing cover and a housing wall of said second filterchamber; and wherein said housing wall of said second filter chamber hasa circumferential sealing groove, said housing cover has a partition fordelimiting said first filter chamber, and said circumferential groovereceives an edge of said partition.
 2. A suction air filter according toclaim 1, wherein an upstream side of one of said filter bodies issubstantially positioned in a plane extending perpendicular to saiddirection of air flow.
 3. A suction air filter according to claim 1,wherein said filter chambers are connected to one another to as to besealed against introduction of external air.
 4. A suction air filteraccording to claim 3, wherein said filter chambers are detachablyconnected to one another.
 5. A suction air filter according to claim 1,wherein said housing wall of said second filter chamber has a pluralityof air-flow openings.
 6. A suction air filter according to claim 5,wherein said air-flow openings are distributed uniformly over the entiresurface area of said housing wall.
 7. A suction air filter according toclaim 1, wherein said second filter chamber comprises a cup-shapedchamber housing with an inner circumferential shoulder at which saidfilter body of said second filter chamber is supported in an air-tightmanner.
 8. A suction air filter according to claim 7, wherein saidfilter body of said second filter chamber comprises a sealing membermade of a foamed plastic material, said sealing member restingair-tightly on said shoulder.
 9. A suction air filter according to claim8, wherein said sealing member is made of polyurethane.
 10. A suctionair filter according to claim 8, wherein said third filter chamber iscomprised of a cup-shaped end housing with a circumferential supportedge for receiving said filter body of said third filter chamber, saidcup-shaped end housing having said outlet opening.
 11. A suction airfilter according to claim 10, wherein said filter body of said thirdfilter chamber comprises a circumferential U-shaped sealing rim thatengages said support edge in an air-tight manner.
 12. A suction airfilter according to claim 11, wherein said sealing rim is sealinglyengaged by said sealing member of said filter body of said second filterchamber.
 13. A suction air filter according to claim 10, wherein saidfilter body of said third filter chamber comprises a rebound containerfor rebounding fuel particles, arranged at a side of said filter body ofsaid third filter chamber facing said outlet opening so as to bepositioned opposite said outlet opening.
 14. A suction air filteraccording to claim 10, wherein said cup-shaped end housing has a sealingsurface facing said second filter chamber and wherein said sealingmember rests sealingly on said sealing surface.
 15. A suction air filteraccording to claim 10, wherein said cup-shaped chamber housing comprisesfastening means for fastening said cup-shaped chamber housing to saidcup-shaped end housing, wherein said fastening means are accessible onlyafter removing said housing cover.
 16. A suction air filter according toclaim 1, wherein said housing cover has a air suction channel forguiding the air sucked in to said first filter chamber, said air suctionchannel having rebound walls for separating coarse dirt particles fromthe air flow.
 17. A suction air filter according to claim 16, whereinsaid inlet opening is located, when viewing said housing cover in an endview, within the area enclosed by the periphery of said housing cover.